Polyether urethane coating composition cured with a di-imine



United States. Patent 3,267,078 POLYETHER URETHANE COATING COMPOSI- TION CURED WITH A DI-IMJNE Adolfas Damusis, Detroit, Mich., assignor to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan No Drawing. Filed Dec. 16, 1963, Ser. No. 330,568

6 Claims. (Cl. 260--77.5)

This invention relates to novel coating compositions and more particularly to stable low temperature-curable polyurethane coating compositions containing blocked NCO-terminated intermediates.

In order to avoid the moisture instability of a onecomponent coating system and the difficulties of a twocomponent coating system, wherein the isocyanate-terminated intermediate and the material containing active hydrogen atoms remain separated until just prior to use, a procedure has been devised in the art for blocking the .isocyanate groups. Blocking is simply a process in which the isocyanate group is reacted with a highly reactive material such as phenol. The use of a blocked isocyanate permits the isocyanate-terminated intermediate and the material containing active hydrogen atoms to be combined in a one-component system which is stable at room temperature. However, the one-component coating systems have the serious disadvantage of requiring high curing temperatures in order to liberate the blocking agent and thus reactivate the NCO groups to form stable urethane linkages with the reactive hydrogen containing compound. This disadvantage becomes extremely important when the material desired to be coated is leather or other heat sensitive materials. Heretofore one-compo nent coating systems containing blocked isocyanate-terminated intermediates could not be used to coat heat sensitive materials. Another disadvantage of one-component coating systems containing blocked isocyanate-terminated intermediates is the relatively long curing time required to obtain a stable coating.

Therefore, it is an object of the present invention to provide a novel coating composition.

Another object is to provide a novel coating composition which is curable by exposure to moisture at room temperature or upon heating.

A still further object is to provide a coating process employing novel coating compositions.

Other objects will become apparent hereinafter.

These and other objects are accomplished by the curable polyurethane coating compositions which comprise on the basis of the total weight of the composition about 25 to 100 weight percent of a blocked isocyanate-terminated polyether-based urethane intermediate wherein said polyether has a molecular weight of about 134 to 6,000, and a diimine, and about 0 to 75 weight percent of an inert solvent.

It has been discovered that, by incorporating certain diimines in coating compositions containing blocked isocyanate-terminated intermediates, the coating compositions will cure in a few hours at room temperature (about 20 C.) without being heated or, alternatively, can be cured in a matter of minutes by heating. Thus, the compositions of this invention represent a one-component coating system which has the unique advantage of curing over a predetermined time period ranging from minutes to hours.

The diimines which are used in the composition of this invention have the formula:

wherein R may be hydrogen, an alkyl radical having from 1 to about 6 carbon atoms or phenyl and A may be an agent such as benzene, toluene or xylene.

'isopentylidene imine) imine).

3,267,078 Patented August 16, 1966 alkylene radical having from 2 to about 6 carbon atoms such as ethylene, tetramethylene, pentamethylene and hexamethylene, or a nonvicinal arylene radical having from about 6 to 12 carbon atoms such as metaand paraphenylene, metaand paradiphenylene, nietaand paraxylylene, and naphthylene. Each of the R groups in the above formula may be the same or different from each of the others. Such diimine compounds are commercially available and may be prepared by reacting a diamine with a carbonyl compound such as a ketone or aldehyde. One such method of preparation is to reflux the carbonyl compound with the diamine in the presence of an azeotroping Some compounds which can be prepared by the above technique and which can be used in the coating compositions of the invention are as follows: 1,2-ethylene bis(isopentylidene imine), 1,2-hexylene bis(isopentylidene imine), l,2-propylene bis(isopentylidene imine), p,p-bisphenylene bis 1,2-ethylene bis(isopropylidene imine), 1,3-pr-opylene bis(isopropylidene imine), p-phenylene bis(isopentylidene imine), m-phenylene bis(isopropylidene imine), and 1,5-naphthylene bis(isopropylidene The following are further illustrative of the compounds which corresopnd to the above formulae and which can be used in this invention:

C=NOHzCI-I N=C on V ofi \CH3 The isocyanate-terminated intermediates which may be employed in the coating compositions of this invention are the product of the reaction of polyether polymers with organic polyisocyanates. The reaction may be carried out either by reaction of a mixture of polyether polymers and organic polyisocyanates or by the sequential reaction :of polyether polymers with organic polyisocyanates. Sequential reaction is necessary in some cases to prevent gelling caused by cross-linking during the reaction. The isocyanate-terminated reaction product is further reacted with a blocking agent such as phenol, cres-ol, ethyl acetyl acetate (diacetic ester), cyclohexanone oxime, or isopropanol to obtain the blocked isocyanate-terminated intermediate. The desired flexibility, impact and abrasion resistance, and solvent resistance of the coating can be obtained by proper control of the equivalent weight, chemical composition, and structure of the intermediates. The polyether polymer is a product of the sequential addition of ethylene oxide, propylene oxide, and/or butylene oxide or mixtures thereof to a polyhydric alcohol until a polymer having a molecular weight of about 134 to 6,000 is produced. For the purpose of defining the present invention, the term polyether polymer includes the polyhydric alcohol itself where its molecular weight is at least 134.

If a polyalkylene ether glycol is used as the polyether polyol in this invention then the polyalkylene ether glycol should have a molecular weight in the range of about 134 to 3,000 in order to impart the more desirable properties in the final urethane composition. Should an alkylene oxide adduct of an alcohol having from 3 to 6 hydroxyl groups be used, then the polyether polyol can have a molecular weight in the range of about 134 to 6,000 which means that a triol could have about 40 oxyalkylene groups per hydroxyl.

The polyhydric alcohol employed in the preparation of the polyether polymers may be an alkanol or phenol and contains about 2 to 6 hydroxy groups and about 3 to 20 carbon atoms, as for example, propylene glycol, diethylene glycol, butane-1,4-diol, pentane-1,5-diol, hexane- 1,3-diol, hexane-1,6-diol, glycerol, 1,1,1-trimethylolprohydroxyldiphenyl dimethyl methane, pentaerythritol, and

sorbitol.

Representative of the typical organic polyisocyanates which may be used in preparing the blocked isocyanateterminated intermediates of this invention are the diisocyanates such as rn-phenylene diisocyanate, toluene-2,4- diisocyanate, hexamethylene-l,6-diisocyanate, tetramethylene-1,4-diisocyanate, cyclohexane1,4-diisocyanate, naphthylene-1,5 -diisocyanate, 1-methoxyphenyl-2,4 diisocyanate, diphenylmethane-4,4-diisocyanate, and 4,4-biphenylene diisocyanate; the triisocyanates such as 4,4,4"- triphenyl methane diisocyanate and toluene 2,4,6-triisocyanate; the tetraisocyanates such as 4,4-dimethyldiphenyl methane 2,2',5,5-tetraisocyanate and mixtures of polyisocyanates.

A typical example of the blocked isocyanate-terminated intermediates which may be employed in the coating compositions of this invention is the product of a process which comprises: first, mixing a polyether polyol with an organic diisocyanate in the proportion of about 2:1 to 3:2, inclusive, mols of polyol to diisocyanate at a temperature of about 20 to 100 C., the preferred range being 80 to 90 C. until a hydroxy-terminated adduct having a substantially constant viscosity is obtained; second, mixing the hydroxy-terminated adduct with about 1 molar proportion of an organic diisocyanate for each hydroxy group of the said adduct at a temperature of about 20 to 70 C., the preferred range being 50 to 60 C., until an NCO-terminated adduct having a substantially constant viscosity is obtained; and third, mixing the NCO-terminated adduct with about 1 molar'proportion of a blocking agent for each NCO group at a temperature of about 80- 100 C. until a blocked NCO-terminated adduct is obtained. The polyether polyol of the reaction can be (a) a straight-chain polyalkylene ether glycol having a molecular weight between about 134 and 3,000, preferably 400 to 1,000, or (b) a branched-chain alkylene oxide addition product of a polyhydric alcohol, said alcohol having at least 3 and not more than about 6 hydroxy groups and said addition product having on an average at least 1 and not more than 40 oxyalkylene groups per hydroxy group. In either case each oxyalkylene group contains about 2 to 4 carbon atoms. The blocking agent can be phenol, cresol, ethyl acetyl acetate (diacetic ester), cyclohexanone oxime or isopropanol.

Another example is the product of the process which comprises: first, mixing a polyether polyol with about 1 molar proportion of an organic polyisocyanate for each hydroxy group of said polyol at a temperature of about 20 to 70 C., the preferred range being 50 to 60 C., to

produce an isocyanate-terminated adduct; second, mixing the isocyanate-terminated adduct with a polyalkylene ether glycol in the proportion of about 2:1 mols of adduct to glycol at a temperature of about 20 to 100 C., the preferred range being 8090 C., to produce a longer chain length NCO-terminated adduct; and third, mixing the NCO-terminated adduct with about 1 molar proportion of a blocking agent for each NCO group until a blocked NCO-terminated adduct is obtained. In this case the polyether polyol is an alkylene oxide addition product of a polyhydric alcohol, said alkanol having at least 2 and not more than 6 hydroxy groups and said addition product having on an average at least 1 and not more than 40 oxyalkylene groups per hydroxy group and each oxyalkylene group contains about 2 to 4 carbon atoms. The polyalkylene ether. glycol should have a molecular weight between about 134 and 3,000. The blocking agent can be phenol, cresol, ethyl acetyl acetate (diacetic ester), cyclohexanone oxime, or isopropanol.

The proportions of blocked isocyanate-terminated intermediate and diimine in the coating compositions may be varied over a Wide range. Since the use of an amine introduces urea linkages to the coating it is possible to impart certain desired properties by careful controlling the quantity of diimine being used. In general, there should be about 0.8 to 2.2 amine equivalents to each isocyanate equivalent. In the primary diamines which are used in the compositions of this invention the equivalent number is, of course, 4. If 0.8 equivalents of diamine are reacted with 1 equivalent of isocyanate then :a branched, NCO- terminated polymer is obtained which is brittle and has a high melting point. Should 2.2 equivalents of diamine be reacted with 1 equivalent of isocyanate then a low melting, flexible, polymer is produced having linear linkages and amine termination.

The solvents employed in the polyurethane coating compositions of this invention must be non-reactive to the blocked isocyanate-terminated urethane intermediates and diirnines. They should be sufliciently low boiling that they will vaporize from the composition when coated onto a surface in a thin film. Many such solvents suitable in general for urethane coatings are known in the art, for example, 2-ethoxyethylacetate, methoxyethylacetate, butoxybutylacetate, toluene, xylene, aniylacetate, other similar esters, ketones, chlorinated solvents, nitroaliphatic solvents, dioxane, and the like.

The portion of solvent may be varied over a wide range. In some instances no solvent is used where a viscous or powdered coating composition is required. Generally, a composition containing about weight percent of blocked isocyanate terminated intermediate and diimine, based on the weight of the over-all composition is a reasonable maximum considering that above this concentration the composition becomes very viscous or is a solid and becomes difficult to apply thus making the formation of good homogeneous films diflicult. A practical lower limit is about 25 weight percent solids (blocked isocyanate terminated intermediate+diimine). Below this an unnecessary quantity of solvent is used and the films formed from lower concentrations are quite thin. In coatings, a preferred composition contains from about 50 to 65 weight percent, based on the weight of the entire composition, of blocked isocyanate terminated intermediate and diimine and about 50 to 35 weight percent of solvent.

The coating process of this invention comprises applying the polyurethane coating compositions presently described to various surfaces by conventional means, such as brushing, spraying, dipping, passing a heated object through the powdered coating composition or coating with a doctor blade. Due to the unique combination of reactants which are used in the compositions of this invention it is not necessary to heat the coating above room temperature in order to cure it. In general, the coatings of this invention will cure at about 20 C. The amount of time needed to cure the coatings at room temperature will vary with the amount of moisture which is in contact with it. That is, the more moisture the shorter the curing time. At a temperature of about 20 C. and 50% relative humidity the coating will cure in about 4 hours. When stored in air-tight containers the application properties of the compounds remain satisfactory for periods exceeding 6 months.

The following examples are presented to illustrate the invention but should not be used to unduly limit the scope of the invention. The molecular weights disclosed in the examples were calculated from the hydroxyl numbers of the compounds.

EXAMPLE 1 Molar Proportions Reaetants Mols Parts Weight Percent Polyoxypropylene adduct of trimethylolpropane Pluracol TP-740 (MW. 723).... 2 1, 446 37. 6

Tolylene diisocyanate (1st portion) TDI (80/20; 2.4/2.6) 1 174 4. 5 Tolylene diisoeyanate (2d portion) 4 696 18. 0 Phenol (1% excess) 4 380 9.8 Diethylcyclohexylamine 0.2% 4 0.1 2ethoxyethyl acetate 576 15. 0 oluene 576 15. 0

Ratio of reactive groups NCO/OH=1.66: .0.

Procedure Stage ].-Polyether polyols used in the reaction are preferably stripped of water by azeotropic distillation with benzene. In this manner, the amount of water can be decreased from 0.08-0.15 to 0.02% or even less.

174 parts of tolylene diisocyanate (TDI) were gradually added into a clean, dry, three-necked five-liter reaction fiask containing 1446 parts of demoisturized Pluracol TP-740 with stirring. The temperature was kept below 90 C. by controlled addition of TDI to the Pluracol TP-740. After the exothermic reaction was finished the contents were heated at 8090 C. and stirred for 3 hours. The abbreviated formula of the hydroxy-terminated intermediate at this stage is:

TP740 TP-740 the circle representing the tolylene diisocyanate molecules, urethane linkages being omitted.

Stage 2.Under a nitrogen blanket 696 parts of tolylene diisocyanate (TDI) were gradually added to the hydroxy-terrninated intermediate. The temperature was 6 kept below 70 C. by controlled addition of TDI to the intermediate. After the exothermic reaction was finished the contents were heated at C. and stirred for 2 hours. The abbreviated formula of the isocyanate-terminated intermediate at this stage is:

O O 0 0. 0 'lP-740 TP-740 the circles representing the tolylene diisocyanate molecules, urethane linkages being omitted.

The isocyanate-terminated intermediate was diluted with 150 parts of 2-ethoxyethyl acetate and 150 parts of toluene to adjust the viscosity of the intermediate.

Stage 3.Technical grade phenol used in the reaction was stripped of water by azeotropic distillation. 380 parts of phenol were diluted with a blend of 81 parts of 2-ethoxyethyl acetate and 81 parts of toluene to make a phenol solution. The 70% solution plus 5% of benzene was charged into a distillation vessel and by azeotropic distillation the moisture was removed with the benzene.

The 70% phenol solution was cooled to 50 C. and added to the isocyanate-terminated intermediate along with 4 parts of diethylcyclohexylamine and heated for 2 hours at C. The abbreviated formula of the blocked isocyanate-terminated intermediate at this stage is:

Ph Ph TP-740 CUP-740 the circles representing the tolylene diiso cyanate molecules, urethane linkages being omitted and Ph representing phenol.

The blocked isocyanate-terminated intermediate was diluted with 345 parts of 2-ethoxyethyl acetate and 345 parts of toluene to adjust the viscosity of the intermediate. The resulting solution was poured into a clean dry bottle and tightly capped.

Properties of NCO-13D-Ph:

NCO/OH 1.66/1.0 Average molecular weight (calc.) 2,684 Average equivalent weight per NCO group, solids 671 Available NCO, percent 6.28

Properties of NCO-13D-Ph solution:

Average weight of solution per equivalent of NCO 958 Percent available NCO, on soln.

'basis 4.38

Brookfield viscosity at 25 C., cps. 7,000-8,500

The following coating compositions were prepared using the above blocked intermediate and various diimines.

Parts by Weight Components Compo- Composition 1 sition 2 (a) Phenol Blocked Isocyanate Terminated Intermediate (NCO1 3D-Ph) 958 958 (1)) CH3 CH3 C=NCHZCH CH CH OHZOH N=O 70 140 OH; OH; OH; OH;

1,6-hexyiene bis(isopentylidene imine) (e) To1uene 66 75 (d) 2-ethoxyethyl acetate 66 75 Amine equivalents per NCO equivalent 1 2 Percent of Qnlirle 5 5 Parts by Weight Components Compo- Composition 1 sition 2 (a) Phenol Blocked Isocyanate Terminated Intermediate (NCO1 3D-Ph) 958 958 (b) CH3 /CH3 C=N CHiCHaN=O 56 112 f3 CH3 CH3 0H3 CH3 1,2-ethylene bis(isopenty1idene imine) (c) Toluene 52 68 (d) Z-ethoxyethyl acetate 52 68 Amine equivalents per N GO equivalent 1 2 Percent of solids 65 65 Parts by Weight Components Compo- Composition 1 sition 2 (a) Phenol Blocked Isoeyanate Terminated Intermediate (N (JO-1- 3D-Ph) 958 958 (b) OH; OH:

/O= N=C\ 101 202 CE /CH CH CH3 CH3 CH3 p,p-biphenylene bis(isopentylidene imine) (c) To1uene 74 91 (d) 2-ethoxyethyl acetate 65 91 Table I shows that excellent coatings cured at loW table reveal that the compositions of this invention not temperatures are attainable Without sacrificing desirable properties. Furthermore, the results presented in the 75 lent pot life and cure time.

TABLE I.-PROPERTIES OF COATINGS FROM ABOVE DESCRIBED COMPOSI- Iroperties A-l A-2 B-1 13-2 (11 C2 D-l D-2 Curing Temperature, C .7 21 20 19 19 24 24 2O 20 Curing Time, hrs. (50% Relative Humidity) 2 2 2 2 2. 2. 5 2. 5 2i 5 Pot Lite, approx. hrs. 48 48 48 47 72 72 72 72 Sword Il'ardness 32 30 28 26 30 42 36 4O Elongation, percent. 120 15 125 65 102 139 43 131 Tensile Strength, 13.3.1 2, 379 2, 609 3, 220 1, 172 3, 528 3, 338 4, 034 3, 769 100% Modulus, p.s.i 1, 890 2, 552 2, 773 2, 740 3, 192 Impact test, Gardner:

Direct (inch-lbs.) 30 30 30 30 30 30 30 30 Indirect (inch-lbs.) 30 30 30 30 30 30 18 30 Softening Point, C 145 145 145 145 145 145 145 145 Solvent Resistance, hr

Toluene 24 24 24 24 24 24 24 24 Oellosolve Acetate 24 8 4 24 12 10 7 Water Resistance:

24 hrs. immersion, 25 C N.E. N.E. N.E. N.E. NiE. N.E. N.E. N.E.

% l1r. immersion, 100 C N.E. N.E. N.E. N.E. N.E. Softens N.E. N.E.

N.E. No Etl'eet.

EXAMPLE 2 Properties of NCO-S-ZD-Ph:

This example illustrates room temperature coating corni gg g ggag" a 3522;; positions prepared from a linear block intermediate as x uivaleni W b opposed to the branched intermediate (NCO-13D-Ph) 5 6 i Welg P r gr 773 described above. The ocedure was used to re are the 0 p Available NCO, percent 5.43

linear block intermediate (NCO5-2D-Ph) was the same as used for NCOl' DPh) described in Example 1. Nonvola'tlle percent 70 Properties of NCO-S-ZD-Ph solution:

Average weight of solution per equivalent 1O NCO 1,104 Molar Pmportions Percent available NCO on soln basis 3 8 Reactor ts NCO5-2DIh 1 Brookfield v1scos1ty at 25 c., cps 4,000-s,000

Mols Parts Ilycight cent The coating compositions shown in Table 1 were pred usi h 'nter ia s rolyoxypmpylem diol Plumcol P4110 pare ng t e above blocked 1 med te and variou (M.W. 42o 2 840 37.82 dllmlnes- Tolylene (liisoeyanate (1st portion) 1 174 7.84 Tolylene diisoeydnte (2d portion)" 2 348 15.66 E Phenol (1% excess) 2 190 8. 55 Diethylcyclohexylalnine (0.2%) 3 0.13 2-ethoxyetl1yl acetate 332 15.00 Components Parts by Toluene 332 15. 00 Weight (a) Phenol Blocked Isoeyanate Terminated Intermediate I (N CO5-2D-]?h) 1, 104 Ratio of reactive groups used in preparation of N00 intermediate NCO/OII=1.5:1.0. (b) CH /CH3 C=N CHzCHz CH2N=C 89. 7

The abbreviated formula of the blocked isocyanateg terminated intermediate is: CH3 CH3 CH3 CH3 1,3-propy1ene bis(is0 ent lidene imine) Ph-OOOPh p y ((01) Tohlilene h 2% 0' et l tt the circles representmg the tolylene dnsocyanate mole- U g z fifi ig NC L5 cules, urethane linkages being omitted and Ph represent- Percentofsollds ing phenol.

Components Parts by Weight (a) Phenol Blocked Isocyanate Terminated Intermediate (NCO-5-2D-P'h) 1, 104

( CH3 CH3 /C=NCHzCH2CH2CHzCH2CH2N=C 70 f3 f5 CH CH CH3 CH3 1,6-hexylene bis(is0pentylidene imine) (e) Toluene 61 (d) 2-ethoxyethylacer1re 61 Amine equivalents per N 00 equivalent 1 Percent of solid Components Parts by Weight (a) Phenol Blocked Isoeyanate Terminated Intermediate (NCO--2D-Ph) 1, 104

(b) 033 CH3 CZNCHZCHZGHZGHZCHZOHQNZO 105 f5 f? CH3 CH3 CH3 H3 1,6-hexylene bis(isopenty1ldeno imine) (c) Toluene 71 (d) 2-ethoxyethyl acetate. 71

Amine equivalents per N GO equivalent 1. 5 Percent of solids 65 TABLE II Coating Properties E F G Curing Temperature, C 20 20 20 Curing Time, hrs. (50% Relative Humidity. 3 3 3 Pot Life (hrs.) 520 460 400 Sword Hardness 34 32 Elongation, percent. 357 215 390 Tensile Strength p s l 3, 517 2, 667 3, 279 30 (100% Modulus (p.s.i) 1, 600 1, 867 1, 443 Impact test, Gardner:

Direct (inch-lbs.) 30 20 30 Indirect (inch-lbs.) 30 4 30 Softening Point, O 145 100 100 Solvent Resistance, hrs.:

Toluene N.E N.E. N.E. Oellosolve Acetate 1 Dissolved 35 Water Resistance:

24 hrs. immersion, 25 C N.E. N.E. N.E. hr. immersion, 100 C Softened Melted Melted N.E5=N0 Effect.

The above data show that excellent coatings cured at room temperature may be prepared from linear as well as branched urethane intermediates.

The compositions of this invention are unique in that they form excellent low temperature curing urethane coatings. They also have good moisture stability as evidenced by their long pot life and are ideally suited for one-component coating systems. Accordingly, the objects of this invention have been met 'by blending a specific type of diimine with blocked isocyanate terminated intermediates.

Iclairn:

1. A polyurethane coating composition which comprises, on the basis of the total weight of the composition, about 25 to 100 weight percent of a diimine and a blocked isocyanate-terminated polyether based urethane intermediate in which said lpo'lyether has a molecular weight of about 134 to 6000, and about 0 to 75 Weight percent of an inert solvent; the amounts of said intermediate and said diimine being such that upon curing of said composition there are present 0.8 to 2.2 amine equivalents for each isocyanate equivalent further-more, said diimine having the formula:

wherein R R R and R are radicals each independently selected from the group consisting of hydrogen, an alkyl having from 1 to 6 carbon atoms and phenyl and wherein A is a member selected from the group consisting of alkylene radicals having from about 2 to 6 carbon atoms and nonvicinal arylene radicals having from carbon atoms. a

2. The composition of claim 1 wherein said blocked NCO-terminated polyether-based urethane intermediate is the product of a process which comprises: first, mixing a polyether :polyol with an organic diisocyanate in the proportion of about 2:1 to 3:2, inclusive, mols of polyol to diisocyanate at a temperature of about 20 to C. until a hydroxy-terminated adduct having a substantially constant viscosity is obtained; second, mixing the hydroxyterminated adduct with about 1 molar proportion of an organic diisocyanate for each hydroxy group of the said adduct at a temperature of about 20 to 70 C. until an NCO-terminated adduct having a substantially constant viscosity is obtained; and third, mixing the NCO-terminated adduct with about 1 molar proportion of a blocking agent for each NCO group until a blocked NCO-terminated adduct is obtained; furthermore, said polyether poly-o1 being a member selected from the group consisting of (a) polyalkylene ether glycols having a molecular weight between about 134 and 3,000 and (b) an alkylene about 6 to 12 oxide addition product of a polyhydric alcohol, said alcohol having about 3 to 20 carbon atoms and at least 3 and not more than 6 hydroxy groups and said addition product having on an average at least 1 and not more than 40 oxyalkylene groups per hydroxy group, and wherein each loxyalkylene group contains about 2 to 4 carbon atoms, and said blocking agent is a member selected from the group consisting Olf phenol, cresol, ethyl acetyl acetate (diacetic ester), cyclohexanone oxime, and isopropanol.

3. The composition of claim 1 wherein said diimine is 1,3-p1'opylene bis(isopentylidene imine).

4. The composition of claim 1 wherein said diimine is 1,6-hexylene bis(isopentylidene imine).

5. The composition of claim 1 wherein said diimine is p,p-biphenylene bistisopentylidene imine).

6. A process of coating a surface which comprises contacting the surface with a composition of claim 1 and curing the composition by exposure to moisture.

References Cited by the Examiner UNITED STATES PATENTS 3,036,020 5/1962 Britain 260-77.5 3,054,757 9/1962 Britain 26077.5 3,127,436 3/1964 Flynn 260-775 3,134,755 5/1964 Muller et al 260-77.5 3,156,658 11/1964 Gmitter 260-775 FOREIGN PATENTS 733,624 7/1955 Great Britain.

LEON I. BERCOVITZ, Primary Examiner. M. C. JACOBS, Assistant Examiner. 

1. A POLYURETHANE COATING COMPOSITION WHICH COMPRISES, ON THE BASIS OF THE TOTAL WEIGHT OF THE COMPOSITION, ABOUT 25 TO 100 WEIGHT PERCENT OF A DIMINE AND A BLOCKED ISOCYNATE-TERMINATED POLYETHER BASED URETHANE INTERMEDIATE IN WHICH SAID POLYETHER HAS A MOLECULAR WEIGHT OF ABOUT 134 TO 6000, AND ABOUT 0 TO 75 WEIGHT PERCENT OF AN INERT SOLVENT; THE AMOUNTS OF SAID INTERMEDIATE AND SAID DIIMINE BEING SUCH THAT UPON CURING OF SAID COMPOSITION THERE ARE PRESENT 0.8 TO 2.2 AMINE EQUIVALENTS FOR EACH ISOCYANATE EQUIVALENT FURTHERMORE, SAID DIIMINE HAVING THE FORMULA: 